The nucleus of an atom has a positive charge equal to Ze
(here Z is atomic number), Z electrons (each with
–e charge) surround the nucleus. These electrons lie
in the atomic orbitals, where each can hold only two electrons.
These atomic orbitals are in turn exist in shells (n = 1, 2,
3….), that round the nucleus. Each shell has
orbitals, which are assembled into
sub shells represented as
and.